Ensuring QoS, i.e. quality of service, in a multiservice IP network, is a well-known challenge often related to IP packets loss due to the problem of network congestion.
In the Lawful Interception scenario, generally speaking it is essential to guarantee the delivery of intercepted payload as Internet Protocol, IP, packets with absolute integrity.
FIG. 1 is a block diagram of an exemplary Lawful Interception, LI, system and network 10 according to prior art. Said system and network comprises a number of entities. The exemplary LI system comprises a Law Enforcement Management Function, LEMF, 12 for requesting LI services of the LI system and collecting the intercepted information of Intercepting Control Elements, ICEs, in the system. The system shall provide access to the intercepted Content of Communications, CC, and Intercept Related Information, IRI, of a target and services related to the target on behalf of one or more Law Enforcement Agencies, LEAs. An intercept request, also denoted Request for LI activation, is sent through a first Handover Interface, HI1, located between the Law Enforcement Management Function 12 and an Intercept Mediation and Delivery Unit, IMDU, 14 comprising a Mediation Function, MF, 16 and an Administration Function, ADMF, 18. Said Mediation Function 16 and Administration Function 18 generates based on said received request a warrant comprising said one or more target identities, and sends said warrant towards an Intercept Access Point, IAP, comprising an Intercepting Control Element, ICE, 20 via an interface denoted X1_1. Requests are also sent from the ADMF to a Mediation Function MF3 in the DF3 on a Handover Interface X1_3. The requests sent on X1_3 are used for activation of Communication Content, and to specify detailed handling options for intercepted CC.
The ICE 20 may be connected to a node of a network, e.g. the Internet, a 3 GMS (third generation Mobile Communications System), etc., from which it intercepts said Content of Communications and Intercept Related Information of a mobile target. Said CC and IRI are network related data. As reference to the standard model, see references [1], [2] and [3], the content of communication is Intercepted in the ICE network node and it is based upon duplication of target communication payload without modification. In reference [3], the interfaces HI1 and HI2 is specified in more detail. The ICE sends IRI raw data via an interface X2 to a Delivery Function for IRI reporting, DF2, 24 and a Mediation Function of IRI, MF2, 22 that generates and delivers to a collection functionality a standardized IRI report based on the received IRI report. Said standardized IRI report is sent over a standardized interface HI2 to the LEMF 12. The ICE 20 also sends CC raw data via an interface X3 to a Delivery Function for CC reporting, DF3, 26 and a Mediation Function IRI, MF3, 28 which generates a delivers to a collection functionality a standardized CC report based on the received CC report. Said standardized CC report is sent over a standardized Interface HI3 to the requesting LEMF 12.
The HI2 and HI3-interfaces represent the interfaces between the LEA and two delivery functions. The delivery functions are used:                to distribute the Intercept Related Information (IRI) to the relevant LEA(s) via HI2;        to distribute the Content of Communication (CC) to the relevant LEA(s) via HI3.        
Together with the delivery functions it is used to hide from the third generation (3G) Intercepting Control Elements ICE(s) that there might be multiple activations by different Lawful Enforcement Agencies on the same target.
FIG. 2 is a more schematic Illustration of a Lawful Interception, LI, system and network than the system and network 10 illustrated in FIG. 1.
An Intercept Access Point, IAP, comprises an Intercepting Control Element, ICE, 20, which is a device within the network that is used for intercepting lawfully authorized Intercept Information sent between a target using some kind of user equipment 40-46 (e.g. mobile phone terminal 40, television set 42, laptop or Personal Computer 44, smartphone 46, etc.) and another user equipment 40-46 or an application server 48, e.g. an Internet TV (IPTV) server, Internet (FTP—File Transfer Protocol) server, etc. in a service center. It may be an existing device that has intercept capability or it could be a special device that is provided for that purpose.
The high bandwidth available in the modern broadband networks puts challenging capacity requirements on the LI Infrastructure and equipment, for both the operator and agency. When the available bandwidth is limited on delivery side, high peaks of traffic on the Incoming side of a DF3 system (see FIG. 3) can cause temporary conditions on the delivery side in which the transmission links can encounter network congestion, which may result into IP packets loss in case of high bandwidth consuming Content of Communication like for instance, IPTV or broadcasting data is to be delivered to a monitoring function.
When the network congestion conditions persist, IP packets loss can take place systematically, with huge degradation in the quality of the provided interception activity. If a Mediation Device, MD, 60 is configured to receive the data from the IAP/ICE 20 and package it in the correct format (which may vary from country to country) and deliver it to the LEA/MC, Law Enforcement Agency/Monitoring center, 80 a congestion problem in the HI3 interface causes IP packet dropping in the MD 60.
One of the measures, requested to the operators as Regulatory Requirements in many countries, is to temporarily buffer the result of interception in the operator domain while reestablishing the delivery of the buffered IP packets when the congestion or link down condition is no longer present. That feature is referred as “Payload Buffering” and a disk buffer 50 may be used.
Although the “Payload Buffering” function is a good solution for emergency conditions like link to the agency down or long congestion status condition due to high peaks of intercepted payload, there are at least three open Issues to be solved:                Real Time Issue: At the prior art, DF3 (26 in FIG. 1) sends IP packets on the HI3 Interface without considering the state of network congestion and without analyzing the priority of processed traffic. Network congestion can involve the problem of the variation of packet delay. That problem is closely associated with quality of service; as example for multimedia conversational services that are real-time characterized, the effect seen could be poor quality in the monitored conversation coming from the jitter.        High Priority LI data: High priority LI data cannot be delivered in real time due to the activated payload buffering functionality, said data will not be available to an agency until the whole buffer 50 is delivered. The contents of any conversational communication activities or the contents of communications related to subscribers that are very sensitive for LEA Investigations are explicitly considered as high priority LI data.        Snowball effect issue: At restore of the normal conditions, the delivery function shall take care of both the buffered LI data and of the real time “fresh” data arriving from the nodes and that situation might potentially trigger a snowball effect with possible loss of data and subsequent delay of the real-time delivery.        